Bubble column-cascade reactor and method

ABSTRACT

A bubble column-cascade reactor comprising a vertical column and a plurality of equidistantly-spaced, horizontally-mounted, uniformly-perforated plates therein, the aperture area of each plate being dependent on the cross-sectional area of the column and the plate-spacing being such that adjacent plates are separated vertically by a distance at least three times the diameter of the columnar reactor. A method for reacting a liquid with a gas or with a non-gaseous reagent in the presence of an inert or reactive gas employing such a bubble column-cascade reactor with little or no liquid back-mixing, dwell time in the reactor being dependent on the liquid and gas throughputs.

tlnited States Patent [191 lass et a1.

BUBBLE COLUMN-CASCADE REACTOR AND METHOD Inventors: Eckhart Blass;Kurt-Henning Koch,

both of Claust l-lal-Zellerfeld; Wolf Cornelius, Werne; Bodo Gross,Unna, all of Germany Schering AG, Berlin and Bergkamen, Germany Filed:Nov. 14, 1972 Appl. No.: 306,199

Assignee:

Foreign Application Priority Data Nov. 22, 1971 Germany 2157736 U.S. Cl423/659, 23/252 R, 23/283, 261/122, 260/448 A, 260/684 Int. Cl. B0lj1/00, C07f 5/06 Field of Search 23/288 E, 283, 284, 285, 23/252 R, 252US; 423/659; 260/448 A, 684; 261/122; 134/25 R References Cited UNITEDSTATES PATENTS Bauer 23/284 X Dec. 10, 1974 2,930,808 3/1960 Zosel23/252 R 3,482,946 12/1969 Shirk 23/284 3,701,793 10/1972 Schmidt et a123/284 X Primary Examiner-Joseph Scovronek Attorney, Agent, orFirm-Curtis, Morris & Safford [57] ABSTRACT A bubble column-cascadereactor comprising a vertical column and a plurality ofequidistantly-spaced, horizontally-mounted, uniformly-perforated platestherein, the aperture area of each plate being dependent on thecross-sectional area of the column and the plate-spacing being such thatadjacent plates are separated vertically by a distance at least threetimes the diameter of the columnar reactor.

A method for reacting a liquid with a gas or with a non-gaseous reagentin the presence of an inert or reactive gas employing such a bubblecolumn-cascade reactor with little or no liquid back-mixing, dwell timein the reactor being dependent on the liquid and gas throughputs.

8 Claims, 3 Drawing Figures BUBBLE COLUMN-CASCADE REACTOR AND METHOD Thepresent invention relates to a bubble columncascade reactor adaptable tothe continuous reaction of a liquid with a gas or with a non-gaseousreagent in the presence of an inert or reactive gas, and to a method foreffecting such a reaction.

An object of the present invention is the continuous reaction of liquidswith gases, or of liquids with liquids in the presence of gases, or ofliquids with solids in the presence of gases, or of liquids with gasesand solids, with a dwell time approaching or corresponding to that in anideal cascade of stirred vessels.

A feature of the present invention is a reactor for carrying out such acontinuous reaction in which the desired dwell time is achieved bycontrol of the throughput of liquid and gas.

A further feature of the present invention is a method for effectingsuch a continuous reaction in such a reactor.

It is already known from German Pat. No. 1,028,096 to attempt to producea gas cushion in a flow-reactor beneath the sieve plates thereof byusing sieve plates whose apertures must be less than 1 millimeter indiameter. However, the patent describes no measures sufficient for thereproducible formation of a gas cushion.

According to the present invention, a liquid reagent is continuouslyreacted with a gas, or with a liquid in the presence of a gas, or with asolid in the presence of a gas, or with a gas and a finely-dividedsolid, by passing the reagents in an upwardly directed parallel flowthrough a tubular flow reactor having perforated plates therein. Byusing an appropriate throughput of liquid and gas, a dwell time in thereactor is sought which approximates or corresponds with that in anideal cascade of stirred vessels.

The tubular flow reactor of the present invention comprises a verticalcolumn having a plurality of perforated plates therein. The totalaperture area of the perforated plates is from 0.5 to 15 percent of theempty reactor cross-section, preferably from 0.5 to 5 percent. Theperforated plates are tightly joined to, i.e., in close contact with,the interior wall of the column and are incorporated in the column in anexactly horizontal position. The individual apertures of each perforatedplate are of the same size and are uniformly distributed over the plate.The distance between two adjacent perforated plates is uniform (i.e.,the plates are equidistant) and is greater than 3 times the diameter ofthe reactor column.

In a preferred embodiment, the apertures are formed as right circularcylinders, which may optionally be beveled at their lower end, i.e., atthe plate bottoms, or may be frustoconical in vertical cross section.

In a further preferred embodiment, a finely-divided solid reagent ispresent in the reagent stream entering the reactor in an amount, inkilograms per hour, which is up to percent of the liquid entering thereactor, in kilograms per hour.

The geometry of the reactor and of the perforated plates according tothe present invention, as well as the volume of the streams of gas andliquid or suspension appropriate thereto, inhibits axial back-mixing ofthe phases between the individual reactor sections defined between theperforated plates. If a stable gas cushion is formed under everyperforated plate, referred to in the following specification as aspecial flow condition," axial back-mixing is completely hindered.

The liquid and gaseous contents of the individual reactor segments areturbulently mixed with one another by the high gas throughput and by theconstant new dispersion of gas in the reaction mixture at the perforatedplates, whereby a high mass transfer is achieved. By reduction of thegas throughput below the minimum value necessary for the formation of agas cushion, the degree of mass transfer is, to be sure, decreased.However, even with a reduction in the gas throughput up to 50 percent ofthis minimum value, back-mixing between the reactor segments is stillsufficiently hindered. A decreased degree of mass transfer has noinfluence on reactions determined by reaction velocity.

In the reactor of the present invention, each reactor segment contains abubble layer whose gas-holdup increases with increasing height of thesegment. If backmixing of liquid is to be completely avoided, then a gascushion like that mentioned earlier is found above the bubble layer andoccupies the space to the floor of the next reactor segment. Each of thereactor segments, thus, is a bubble column reactor so that the completereactor can be characterized as a bubble columncascade reactor.

lf back-mixing of liquid or of a suspension through the apertures of theperforated plates is reduced to a minimum or completely hindered byformation of a gas cushion, by means of a correspondingly chosen volumeof the gas stream, then the bubble column-cascade reactor of theinvention has the same dwell time as an ideal cascade of stirredvessels, since the gas simultaneously effects good mixing of the liquidin the individual reactor segments.

It is known in the art that an ideal cascade of stirred vessels has anideal mixture of the liquid reagent present in each stirred vessel andthat back-mixing between the separate stirred vessels is impossible.Still, a slight back-mixing of liquid or of suspension through theapertures of the perforated plates in the reactor of the presentinvention similarly has no measurable influence on the dwell timebehavior.

Since the bubble column-cascade reactor of the invention behaves, fromthe point of view of the dwell time, like a cascade of stirred vessels,well-known equations can be applied to the system for calculating anddetermining average dwell time and, therewith, for achieving anindependence of the reactor contents from the required productthroughput [cf. J. Kardos, Chemische Technik 4, 216 220 (i969) and S,275 280 (1969)]. With the process and reactor of the present invention,the same dwell time as in an ideal cascade of stirred vessels can beachieved with a considerably reduced technical outlay. In addition, itis possible at will to produce long dwell times ofa liquid or suspensionin the reactor.

A better understanding of the present invention will be had by referringto the drawing, wherein FIG. 1 is a schematic drawing ofa reactionsystem incorporating a reactor (shown in a side section view) accordingto the present invention;

FIG. 2 is a plan view of a perforated plate for use in such a reactor;and

FIGS. 3A 3C are side sectional views showing preferred apertureconfigurations.

H6. 1 shows reactor 11 comprising cylindrical column 12 having therein aplurality of perforated plates 13 equidistantly spaced from each other.Gas, moved by means such as compressor 14, enters reactor 11, throughline 15, at the reactor bottom 16, beneath lowermost perforated plate17. Liquid, or a suspension of a solid in a liquid, enters reactor 11,through line 18, at 19, above lowermost plate 17. The liquid is moved bymeans such as pump 20.

Within column 12, plates 13 are suitable movably mounted on central core21, which may be tubular for example. Plates 13 are in close contactwith core 21 and, on their periphery, with the inner wall of column 12.Asbest seen in FIG. 2, plates 13 may be provided with a peripheralgasket of a reaction-resistant material such as fluorinated rubber orsteel.

Above topmost perforated plate 22, a mixture of gas and liquid, or ofgas and suspension, is withdrawn from reactor 11 and led to separator23. The gas is returned to reactor 11 through line 24 to circulatingcompressor 14. Additional gas is introduced into the circulating gasstream at 25 as necessary. Liquid or suspension is removed fromseparator 23 through line 26.

. t ln'the reactor segments defined between adjacent plate s'13, theheight of bubble layer 27 and, therewith, o f'g'as cushion 28, can beadjusted by changes in the volume of the gas and/or fluid streamsthrough valves 29and 30, respectively. I

FR 2 is a plan view of a perforated plate 13 showing a suitable uniformdistribution of apertures 31, all of thefsame size.

"FlG. 3A is a side view, in section, ofa preferred apertureconfiguration in which the apertures have a right circular cylindricalsection.

FIG. 3B is a side view, in section, of another preferred apertureconfiguration in which the circular apertures are beveled at their lowerends, i.e. on the bottom of plates 13.

FIG. 3C is a side view, in section, of still another preferredapertureconfiguration in which the apertures are frusto-conical in verticalsection.

The reactor diameter, the spacing of the perforated plates, the numberof perforations and their diameter, the distribution of theperforations, and the thickness of the plates and their gasketing, onthe one hand, and the volume of the liquid and gas streams and thephysical properties of the gas and liquids such as density, viscosity,and surface tension, on the other hand, influence the formation of a gascushion and the degree of back-mixing of the liquid in the reactor.

It has been found that for each geometry of the perforated plates andreactor and at a given value of liquid throughput, there is acharacteristic gas throughput at which there is no back-mixing throughthe perforated plates'and a gas cushion is formed under the perforatedplates. This flow condition is characterized as the special flowcondition."

At a constant aperture diameter and at a constant aperture number, thegas throughput necessary for reaching the special flow conditiondecreases with increasing liquid throughput, while simultaneously theliquid content in the individual reactor segments increases and thethickness of the gas cushion decreases. With the following definitionsof the Reynolds numbers for the liquid and gas phase at a given aperturediameter, do

m m X X PL I and ad 011 X 41 X pG/nG,

the following is the condition for gas cushion formation:

Rent/Read 1 (For gases with very low densities, p there is a significantdeparture from the aforementioned relationship.)

The loss in gas pressure in the bubble columncascade reactor of theinvention is given with an error of :5 percent for all material pairsand geometries investigated, and for all possible flow conditions, bythe empirical relationship given below. With a definition of the Froudenumber at a given reactor diameter, D,

00 00 X Pa/ X S X (PL Po), the following equation is valid in the region3 X 10' Fr 10*.

The pressure loss coefficient, s, can be determined by means of thefollowing dimensionless relationship:

The symbols employed in these equations have the following meaning:

d Aperture diameter D Reactor diameter g Gravitational constant hSpacing between adjacent perforated plates n Number of reactor segmentsAp Pressure loss w Velocity 6 Pressure loss coefficient 1; Dynamicviscosity p Density 4) Relative free aperture area Fr Froude number ReReynolds number Subscripts:

d pertains to the aperture diameter D pertains to the reactor diameter 6pertains to the gas phase L pertains to the liquid phase The bubblecolumn-cascade reactor according to the invention and the formation ofgas cushions therein was first examined with model substances (Table l)and then chemical reactions were investigated (cf. Table ll).Observations of gas cushion formation and of backmixing were made usinga transparent model.

The process of the present invention can be used to particular advantagefor the preparation of metal organic compounds, particularly for thepreparation of aluminum organic compounds according to the Zieglerprocess. in this process, finely-divided aluminum is reacted withhydrogen in the presence of aluminum trialkyls and, optionally, olefins.Other reactions involve the preparation of aluminum trialkyls fromdialkyl aluminum hydrides and olefins.

As an example of reactions involving a liquid with a gas according tothe present invention, the preparation of triethylaluminum fromdiethylaluminum hydride and 3 ,85 3 ,9 86 6 ethylene can be mentioned. Areaction between a liquid, a reactive solid, and a reactive gas isexemplified by the reaction of aluminum with triethylaluminum andhydrogen to form diethylaluminum hydride. In similar fashion, a liquidcan be reacted with another liquid or 5 4. A reactor as in claim 3wherein said right circular cylindrical apertures are beveled at theirlower end.

' 5. A reactor as in claim 1 wherein said apertures are frusto-conicalin vertical cross-section.

6. A method for continuously reacting a liquid with with a solid in thepresence of an inert gas such as nitroa gas which comprises flowing saidliquid and gas upgen or carbon dioxide, where employment of thereacwardly through a walled vertically columnar reaction tor or reactionmethod of the invention would be adzone separated into a plurality ofreaction compartvantageous. ments by perforated plates equidistantlystacked ex- The tests reported in Table I below were performed actlyhorizontally in said reaction zone. adjacent plates in a column 3 metershigh equipped with 4 plates. The being separated vertically by adistance at least three reactor was at a temperature of 20C., and thegas prestimes the diameter of said columnar reaction zone and sure wasone atmosphere (STP). being tightly joined to the interior wall thereof.each The tests reported in Table 11 below were performed plate having aplurality of apertures therein of the same with a liquid content in thereactor of 60 percent and size distributed uniformly over the area ofthe plate, the

with a gas cushion height of mm. total free aperture area of the platesbeing from 0.5

TABLE I Tests with Model Substances in a Bubble ColumnCascade ReactorAverage Gas Liquid Gas Aperture Diameter/ Aperture Dwell Liquid CushionThroughput Throughput Column Diameter Area Time Content Height Liquid(kg/hr) Gas (kg/hr) (mm/mm) (70) (hrs) (mm) 1) Dibutyl ether 21.8 N 38.54/140 249 0.9 50 100 2) Octene 13.8 N, 17.2 2/140 1.6 1.5 57 55 3) Water46.4 Air 35.5 4/140 2.5 0.55 50 80 4) Water 45.8 Air 14.8 2/140 1.6 0.6559 40 5) Water 29.2 Air 12.0 4/140 1.25 1.1 66 6) Water 46.9 Air 4.04/140 2.5 0.93 87 0 0 7) Water 46.9 Air 11.9 4/140 2.5 0.7 65 15 8)Water 46.9 Air 19.0 4/140 2.5 0.62 58 9) Water 46.9 Air 33.4 4/140 2.50.51 48 70 Total aperture area of the plates as a percentage of thecrnss-seetional area of the empty reactor.

TABLE 11 Tests with Chemical Reagents in a Bubble Column-Cascade ReactorColumn Liquid Pressure/ Average Height/ or Solid Liquid Gas TemperatureAperture Diameter/ Aperture Dwell No. of Liquid Throughput Throughput(atm STP/ Column Diameter Area" Time Plates Suspension (kg/hr) Gas(kg/hr) C.) (mm/mm) (70) (hrs) (m/-) 10) DEAH 19.8 Ethylene 13.1 7.5/1003/70.3 3.4 0.51 5.5/12 11) TEA. A1 15.0 Hydrogen 9.65 150/100 4.5/1002.4 2 6.55/12 12) DEAH 406 Ethylene 355 10/100 31/300 3 0.75 10/10 13)TEA. A1 236 Hydrogen 122 150/140 5/300 4 2 12/14 DEAH diethylaluminumhydride TEA triethyluluminum A1 aluminum powder Total aperture area ofthe plates us a percentage of the cross-sectional area of the emptyreactor ,wh i l i d i percent to 15 percent of the cross-sectional areaof said 1. A bubble column-cascade reactor for continuously columnar f lZone lheflow of gas and llquld reacting a liquid with a gas or with anon-gaseous reathrough 531d reaction Zone bemg Such gent in the presenceof an inert or reactive gas, said reactor comprising a vertical columnhaving a plurality of perforated plates equidistantly stacked exactlyhorizon- WherePy a gas cushlon formed unde-r plates and tally withinsaid column, adjacent plates being separated vertically by a distance atleast 3 times the diameter of the reactor, said plates being tightlyjoined to the Reynolds numberm/Reynolds number 0.1,

Reynolds number w X d X p /nL,

interior wall of said reactor, each plate having a plural- Reynoldsnumber X d X pG/nc ity of apertures therein of the same size distributeduniw velocity formly over the area of the plate, the total free apertured aperture diameter area of the plates being from 0.5 percent to 15percent p density of the cross-sectional area of the empty reactor. 1;dynamic viscosity 2. A reactor as in claim 1 wherein the total freeaperand the subscripts d, G, and L refer respectively to apture area ofthe plates is from 0.5 to 5 percent of the erture diameter, the gasphase, and the liquid phase. cross-sectional area of the empty reactor.7. A method for continuously reacting a liquid with 3. A reactor as inclaim 1 wherein said apertures are a non-gaseous reagent in the presenceof a gas which right circular cylindrical in vertical cross-section.comprises flowing said liquid, gas, and non-gaseous reagent upwardlythrough a walled vertically columnar reaction zone separated into aplurality of reaction compartments by perforated plates equidistantlystacked exactly. horizontally in said reaction zone, adjacent platesbeing separated vertically by a distance at least three times thediameter of said columnar reaction zone and being tightly joined to theinterior wall thereof, each plate having a plurality of aperturestherein of the same size distributed uniformly over the area of theplate, the total free aperture area of the plates being from 0.5 percentto percent of the cross-sectional area of said columnar reaction zone,the flow of gas and liquid through said reaction zone being such thatReynolds numbcr /Reynolds number 0.1,

whereby a gas cushion is formed under said plates, and wherein Reynoldsnumber w X d X p /n Reynolds number w d X p /n

1. A BUBBLE COLUMN-CASCADE REACTOR FOR CONTINUOUSLY REACTING A LIQUIDWITH A GAS OR WITH A NON-GASEOUS REAGENT IN THE PRESENCE OF AN INERT ORREACTIVE GAS, SAID REACTOR COMPRISING A VERTICAL COLUMN HAVING APLURALITY OF PERFORATED PLATES EQUIDISTANTLY STACKED EXACTLYHORIZONTALLY WITHIN SAID COLUMN, ADJACENT PLATES BEING SEPARATEDVERTICALLY BY A DISTANCE AT LEAST 3 TIMES THE DIAMETER OF THE REACTOR,SAID PLATES BEING TIGHTLY JOINED TO THE INTERIOR WALL OF SAID REACTOR,EACH PLATE HAVING A PLURALITY OF APERTURES THEREIN OF THE SAME SIZEDISTRIBUTED UNIFORMLY OVER THE AREA OF THE PLATE, THE TOTAL FREEAPERTURE AREA OF THE PLATES BEING FROM 0.5 PERCENT TO 15 PERCENT OF THECROSS-SECTIONAL AREA OF THE EMPTY REACTOR.
 2. A reactor as in claim 1wherein the total free aperture area of the plates is from 0.5 to 5percent of the cross-sectional area of the empty reactor.
 3. A reactoras in claim 1 wherein said apertures are right circular cylindrical invertical cross-section.
 4. A reactor as in claim 3 wherein said rightcircular cylindrical apertures are beveled at their lower end.
 5. Areactor as in claim 1 wherein said apertures are frusto-conical invertical cross-section.
 6. A method for continuously reacting a liquidwith a gas which comprises flowing said liquid and gas upwardly througha walled vertically columnar reaction zone separated into a plurality ofreaction compartments by perforated plates equidistantly stacked exactlyhorizontally in said reaction zone, adjacent plates being separatedvertically by a distance at least three times the diameter of saidcolumnar reaction zone and being tightly joined to the interior wallthereof, each plate having a plurality of apertures therein of the samesize distributed uniformly over the area of the plate, the total freeaperture area of the plates being from 0.5 percent to 15 percent of thecross-sectional area of said columnar reaction zone, the flow of gas andliquid through said reaction zone being such that ReynoldsnumberLd/Reynolds numberGd 0.1, whereby a gas cushion is formed undersaid plates, and wherein Reynolds numberLd wLd X d X Rho L/ eta L,Reynolds numberGd wGd X d X Rho G/ eta G, w velocity d aperture diameterRho density eta dynamic viscosity and the subscripts d, G, and L referrespectively to aperture diameter, the gas phase, and the liquid phase.7. A method for continuously reacting a liquid with a non-gaseousreagent in the presence of a gas which comprises flowing said liquid,gas, and non-gaseous reagent upwardly through a walled verticallycolumnar reaction zone separated into a plurality of reactioncompartments by perforated plates equidistantly stacked exactlyhorizontally in said reaction zone, adjacent plates being separatedvertically by a distance at least three times the diameter of saidcolumnar reaction zone and being tightly joined to the interior wallthereof, each plate having a plurality of apertures therein of the samesize distributed uniformly over the area of the plate, the total freeaperture area of the plates being from 0.5 percent to 15 percent of thecross-sectional area of said columnar reaction zone, the flow of gas andliquid through said reaction zone being such that ReynoldsnumberLd/Reynolds numberGd 0.1, whereby a gas cushion is formed undersaid plates, and wherein Reynolds numberLd wLd X d X Rho L/ eta L,Reynolds numberGd wGd X d X Rho G/ eta G, w velocity D aperture diameterRho density eta dynamic viscosity and the subscripts d, G, and L referrespectively to aperture diameter, the gas phase, and the liquid phase.8. A method as in claim 7 wherein said non-gaseous reagent is a finelydivided solid entering the reaction zone in an amount by weight, perunit time, which is up to 15 percent of the weight of liquid enteringthe reaction zone per unit time.